Heart valve disease continues to be a significant cause of morbidity and mortality, resulting from a number of ailments including rheumatic fever and birth defects. Cardiovascular disease is the number one cause of death, killing more than 600,000 Americans each year. According to the American Heart Association, more than five million Americans are diagnosed with heart valve disease each year. Heart valve disease can occur in any single valve or a combination of the four valves, but diseases of the aortic and mitral valves are the most common, affecting more than five percent of the population. An estimated 85,000 aortic valve replacement procedures are performed every year in the U.S. Worldwide, approximately 300,000 heart valve replacement surgeries are performed annually. About one-half of these patients receive bioprosthetic heart valve replacements, which utilize biologically derived tissues for flexible fluid occluding leaflets.
The most successful bioprosthetic materials for flexible leaflets are whole porcine valves and separate leaflets made from bovine pericardium stitched together to form a tri-leaflet valve. The most common flexible leaflet valve construction includes three leaflets mounted to commissure posts around a peripheral support structure with free edges that project toward an outflow direction and meet or coapt in the middle of the flowstream. A suture-permeable sewing ring is provided around the inflow end. Various tissue treatments extend the life of the heart valve, such as by reducing calcification, thus deferring the need for a second surgery to replace the first implanted valve. The use of glutaradehyde in such tissue treatments has been proven effective in avoiding resorption of the treated tissue after implantation.
Bioprosthetic heart valves are conventionally packaged in jars filled with preserving solution for shipping and storage prior to use in the operating theater. The preserving solution maintains the functionality of the bioprosthetic tissue within the heart valve. Glutaraldehyde and formaldehyde are widely used as storage solutions due to their sterilant properties.
Prosthetic heart valves may be implanted independently in one of the orifices or annuluses of the heart, or may be coupled to a flow conduit which extends in line with the valve a predetermined distance. For example, the Carpentier-Edwards® Bioprosthetic Valved Conduit available from Edwards Lifesciences of Irvine, Calif. features a porcine bioprosthetic heart valve to which are coupled both and inflow and outflow woven polyester extensions. The Edwards valved conduit is particularly well-suited for treatment of a malfunctioning pulmonic valve. Other valved conduits are designed for reconstruction of portions of the flow passage above and below the aortic valve, such as the ascending aorta, in addition to replacing the function of the valve itself. There are also other applications for valved conduits, such as to provide a bypass flow path connecting the apex of the heart directly to the descending aorta. Prior bioprosthetic valved conduits, as with bioprosthetic heart valves, are stored in a liquid preserving solution, and thus the conduits are formed of woven polyester without a bioresorbable sealant. Although such conduits are suitable in certain situations, and tend to seal relatively quickly in the body from tissue ingrowth, too much blood can initially seep through their walls after implant which may be detrimental. Uncoated fabric such as polyethylene terephthalate (PET) has a high leakage rate, and thus the surgeon needs to pre-clot the graft with patient's blood before use. Nevertheless, such grafts still produce unacceptable leaking. Others have proposed using a non-bioresorbable sealant layer, such as silicone in U.S. Patent Publication No. 2008/0147171 to Ashton, et al., published Jun. 19, 2008, but such layered conduits tend to be relatively thick walled and not very flexible, and so are not preferred.
Consequently, some surgeons prefer conduits or grafts in which porous tubular structures such as woven polyester (e.g., Dacron) are impregnated with bioresorbable materials such as gelatin, collagen or albumin. These conduits are not porous initially, and thus prevent blood loss, but the sealant medium eventually degrades by hydrolysis when exposed to water after implant and are replaced by natural tissue ingrowth. Gelatin in the graft can also be treated in such a way as to cause cross links to form between the amino groups present in the gelatin molecules, which renders the gelatin more resistant to hydrolysis. Methods of forming such grafts are seen in U.S. Pat. No. 4,747,848 to Maini, issued May 31, 1988.
Unfortunately, it is not possible to pre-assemble conduits or grafts sealed using bioresorbable materials with bioprosthetic heart valves because of storage complications. That is, the liquid sterilant in which tissue valves are stored will eventually wash the bioresorbable sealing medium (gelatin, collagen, albumin, etc.) out of the permeable conduit material. Because of the benefits of using sealed conduits or grafts and the positive attributes of bioprosthetic heart valves, some surgeons couple the two components together at the time of surgery—post-storage. That is, technicians in the operating theater connect the sealed conduit which has been stored dry to the bioprosthetic heart valve which has been stored wet. Such assemblies can be seen in U.S. Patent Publication No. 2010/0274351 to Rolando, et al., published Oct. 28, 2010, and in U.S. Pat. No. 7,575,592 to Woo, et al., issued Aug. 18, 2009. The sealed conduit may be sewn to the sewing ring of the bioprosthetic heart valve, or some other form of quick-connect coupling can be provided, such as seen in U.S. Patent Publication No. 2006/0085060 to Campbell, published Apr. 20, 2006. Although these assemblies are in theory the best of both worlds, the time and effort required to connect a sealed conduit with a bioprosthetic heart valve creates problems in the high-pressure environment of the cardiac operating theater. Adding to the complexity of the connection procedure, the biological valve must be kept damp to avoid degradation of the tissue, while the graft must be kept dry to avoid initiating hydrolysis. Further, prolonged exposure of the valve and conduit in the operating room prior to implantation increases the chance of infection. For aortic conduits, even a small leak in this connection can be fatal because the pressure is so high. So the implanting surgeon has to sew these components together quickly without any leaks.
Accordingly, there is a need for a valved conduit having a bioprosthetic tissue valve and a conduit or graft preferably sealed using a bioresorbable material which is simpler to prepare and deploy in the operating room.